Preparation of aromatics from petroleum distillates



March 13, 1951 E; T. L AYNG PREPARATION 0F AROMATICS FROM PETROLEUM DISTILLATES Original Filed Sept. 27, 1940 catalyst at a. feed rate and under other reaction conditions adapted to convert the aliphatic compounds present in the naphtha to aromatic com- The gaseous fraction withdrawn overhead through line II contained a relatively large amount of hydrogen, amounting to about 60%, the remaining constituents being normally gas- 5 eous hydrocarbons containing 1'. to 3 carbon atoms.

pounds, such as benzene, toluene', and xylene, to-

gether with a certain amountpf olenic' hydrocarbons, and various other hydrocarbons resulting from the limited amount :of thermal decomposition which takes place. Tower I is prefer- In addition to gaseousand liquid products, a small amount of carbonaceous material was deposited on the catalyst amounting to 0.6% by weight of the charge.

The deaotivating deposit of carbonaceous material on the catalyst was removed after the onstream period by an oxygen-containing gas sup- ,plied through line 39 and withdrawn through ably maintained under a suitable degree of sul peratmospheric pressure. The particular operating conditions employed in this stage of the process, charging stock, and catalyst, may fsuitably correspond to those disclosed and claimed in co-pending application Serial No. 294,784, led

rSeptember 13, 1939, now Patent No. 2,320,147 issued May 25, 1943, the latter applicationvbeing directed primarily to the production of a highly aromatic naphtha especially suitable for use as a high quality antiknock motor fuel. Thus, for example, the followingconditions may be employed: a temperature between about 875 F. and

about 1075 F., a total pressureof the order of 50 to 450 pounds per square inch, a mol ratio of hydrogen to naptha charged between about 0.5 and about 8 and a space velocity of 0.05 to 5.0

'volumes oi liquid hydrocarbons charged pervoll .ume of catalyst space per hour;

From tower 'I the conversion products ,are withdrawn through line e and pass through" a condenser 9 and then into 'ahi'gh pressure separator lil.` The pressure Within' separatori!) suitably controlled by valve I3 to separate the total conversion products into normally gaseous constituents, including hydrogen and gaseous hydrocarbons containing 1 to 3 carbon atoms and into normally liquid constituents',` the gaseous fraction being withdrawn overheadV through line I I and the liquid productfrom the bottom of the separator through'linel.-

A portion of 4the hydr'oger1-containing gas withdrawn through line' II is added to the naphtha feed to tower?, by recirculating it by compressor I4 through linev5, the quantity thus circulated being regulatedby vali/e151 Operating. conditions suitably maintained in the first stage of the catalytic treatment in catalyst tower T, are illustrated by the following example of the -conversion of a 44 octane number naphtha having an initial boiling point of 240 F., an end point of 418 F., and an, A. P. I. gravity of 51.4, overa molybdenum oxide-alumina catalyst wherein the following conditions were maintained in the catalyst tower I:

Exemple Temperature, inlet of reactor... JF... 1015 Temperature, outlet ofreactor F 4 925 Pressure lbs./sqlin' 300 Feed rate Y A vols. naphtha/hn/voLof catalyst-- 0.75

Hydrogen gas recycle l cu. ft./bbl. of naphtha--. -2600 Length of on-stream period hrs-- 6 of 80 C. F. R. M.`, and containing approximatelyVy 7.5% by volume of toluene.

'similar arrangement of multiple reactors and regeneration means, lines 4l and 48, for introducing and withdrawing an oxygen-containing gas are likewise used with respect to the second catalytic reactor 26.

The hydrogen-containing stream of gas from line I I is preferably split, a portion being utilized for recycling through line 5, and another portion is forwarded through line 27' for"use in the seoond catalytic stage, the net hydrogen Aproduced being withdrawn through line' 4l.

o The operating conditions maintained in reactor 'I, indicated bythe ioregoing example are preferably of substantially less severity than those maintained in the second stage of catalytic'treat- Vmenteiecte'din catalyst tower`2u`. The maintenance of this difference in yrelative severitylias been found to be highly advantageous since a high yield of toluene, aswell as av hydrogen-containing' gas of relatively'liigh hydrogen concentration, are 'thus produced in the rst stage of the process, and both of these factors areimportant in the securing of the best results in the second catalytic stage.

The liquid productv withdrawn through line" I2,

or a portion thereof, is passed by line 2l to a suitable fractionator. I6 wherein a close boiling toluene-rich cut containing as large a proportion of Vtoluene as maybe satisfactorily separated is withdrawn as a side stream through line I'I 'and passed to a side stream stripper I8. A suitable stripping medium such as steam is supplied' to the -bottom of the side stream stripper through line IS-to further increase the concentration of toluene by removal of lighter boiling components,

`'these components and stripping medium-being withdrawn overhead from the stripper through line 20 and returned to the upper portion of the fractionaton The overhead product from fractionator I6'is withdrawn through line 42, condensed in condenser 43, and sent to gasoline storage through line 44. The bottom fraction withdrawn through line 45,' together with any portion of the total liquid withdrawn by line 4S from separator I0 not required for the produc- "ton of 1301113161 is'likewise sent to gasoline stoy l age through'line 44.

Afraction relatively rich in toluene is 'thus `'produced and withdrawn from the bottom of side stripper I8 through line2I`. lIn addition to toluene, this fraction oontains'non-aromatic hydrocarbons Vwhich `are Aextremely dilicult to sepay ratefrml the toluene 'to tlre'extent required for :the production of substantially pure tolener by any commercially available methods such as frac,

fins, are Withdrawn respectively, from the bottom of the reactor through line 3l, and overhead through line 38. The overhead fraction is condensed in condenser 49 and may suitably be sent to gasoline storage through line 44 together with the bottoms fractionfwithdrawn through line 3l.

Toluene thus separated is usually in suiilcient the invention may be practiced generally with any dehydrogenating and cyclicizing' catalyst. For example, oxides or suldes of the metals included within the lefthand column of Group VI of the periodic table, and other metal compounds, particularly oxides of the metals of the lefthand column of groups IV and V of the periodic table, such as titanium, cerium, thorium, and vanadium. Moreover, While these compounds may be used alone or on various supports or carriers, I regard it highly preferable to utilize them supported on alumina, particularly activated alumina.

While my invention has been described particularly with reference to the production of substantially pure toluene, it is apparent that it may also be applied with suitable modifications to the production of substantially pure benzene, or xylene from hydrocarbon mixtures consisting largely of one of these compounds but, as in the case of the toluene-rich fraction, contaminated with non-aromatic hydrocarbons differing only slightly in their boiling points from the particular aromatic compounds to be isolated. In case benzene is the compound to be isolated, I prefer to employ somewhat more servere operating conditions in the secondstage than in the case of toluene-rich fractions, and in the case of xylene somewhat milder conditions, but in either case,A

the operating conditions are preferably of subin the first catalytic stage.

It is further apparent, that while the preferred mode for the practice of my invention contemplates a combination of two stages of catalytic conversion the invention is applicable generally to the isolation of toluene, or other aromatic compounds, from hydrocarbon mixtures rich in the desired aromatic compound and contaminated with non-aromatic compounds differing only slightly in boiling range, regardless of the source of such mixtures.

Iclaim: Y

1. A method of producing substantially pure toluene which comprises passing a naphtha including a large proportion of non-aromatic hydrocarbons containing from 6 to 12 carbon atoms in the presence of added hydrogen in contact at an elevated temperature with a dehydrogenating and cyclicizing catalyst to produce hydrogen and largely convert said non-aromatic compounds to aromatic compounds including a substantial amount of toluene, fractionating the mixture thus produced to separate a toluene-rich fraction including at least 50% toluene together with non-aromatic hydrocarbons containing 6 or more carbon atoms, passing the toluene-rich fraction in contact at an elevated temperature within the range of 950 to l025 F. with adehydrogenating and cyclicizing` catalyst in the presence of added hydrogen and under reaction conditions of substantially greater severity cor-y responding to a temperature increase of at least about 50 F. higher than those maintained in the iirst `stage and to an extent such that at least of the normally liquid hydrocarbons thus produced are aromatic, and fractionating substantially pure toluene from the mixture thus produced.

, 2. A method of producing substantially pure toluene which comprises passing a naphtha in cluding a mixture of aliphatic hydrocarbons containing from 6 to 12 carbon atoms in the presence of added hydrogen in contact at an elevated temperature with a dehydrogenating and cyclicizing catalyst to produce hydrogen and largely convert said aliphatic compounds to aromatic compounds including a substantial amount of toluene, fractionating the mixture thus produced to separate a toluene-rich fraction including at least 75% toluene together with non-aromatic hydrocarbons containing 6 or more carbon atoms, passing the toluene-rich fraction in contact at an elevated temperature at least 50 F. higher than the temperature maintained in the initial contacting stage with a dehydrogenating and cyclicizing catalyst in the presence` of added hydrogen and under reaction conditions of substantially greater severity than those maintained in the iirst stage and adapted to convert said non-aromatic hydrocarbons to an extent such that at least 90% of the normally liquid hydrocarbons thus produced are aromatic, and fractionating substantially pure toluene from the mixture thus produced.

3. A method ol producing substantially pure toluene which comprises passing a naphtha including a mixture of aliphatic hydrocarbons containing from 6 to 12 carbon atoms in the presence of added hydrogen in contact at an eleyated temperature with a dehydrogenating and cyclicizing catalyst to produce hydrogen and largely convert said aliphatic compounds to aromatic compounds including a substantial amount 0f toluene, fractionating the mixture' thus produced to separate a toluene-rich fraction boiling Within the range of about 220 to 240" F. including at least 50% toluene together with nonaromatic hydrocarbons containing 6 or more carbon atoms, passing the toluene-rich fraction in Contact at an elevated temperature between 9500 and 1025o F. with a dehydrogenating and cyclicizlng catalyst in the presence of added hydrogen produced in said rst stage and under reaction conditions of substantially greater severity than those maintained in the first stage corresponding to a temperature increase of at least 50 F., and fractionating substantially pure toluene from the mixture thus produced.

4. A method for producing substantially pure toluene which comprises passing a naphtha including a large proportion of non-aromatic compounds containing from 6 to l2 carbon atoms in the presence oi added hydrogen in contact at an elevated temperature with a dehydrogenating and cyclicizing catalyst to produce hydrogen and largely convert said non-aromatic compounds to aromatic compounds including a substantial amount of toluene, fractionating the mixture thus produced to separate a toluene-rich fraction including at least 50 per cent toluene together with non-aromatic hydrocarbons containing 6 or more carbon atoms, passing the toluene-rich fraction in contact at an elevated temperature with a dehydrogenating and cyclicizing catalyst in the presence of added hydrogen .inrststage corresponding to .a sdecrease iinspace `velocity. -of at least one-half, .and fractionating Asubstantially pure toluene from the mixtureithus produced.

5. A process for -t-he production of a substantially ,pure 'desired .aromatic :compound kwhich comprises passing a naphtha including a large proportion `of non-aromatic compounds containing from 6 to l2 carlooneatoms inztlrepresenceaof :added hydrogen iin conta-ct iat an ielevatedftemperature with a dehydrcgenatingand 'cyclicizing catalyst to produce hydrogen land `,largely 'convert said non-aromatic compounds to iaromatic com-.-

pounds including a substantial amount of the desired aromatic compound, fractionating the mixture thus produced to separate a fraction rich in the desired aromatic compound including at least 50 per cent of the desired aromatic compound together with non-aromatic hydrocarbons containing 6 or more carbon atoms, passing the thus separated fraction rich in the desired aromatic compound in contact at an elevated temperature with a dehydrogenating and cyclicizing catalyst in the presence of added hydrogen to convert said non-aromatic compounds to aromatic compounds under reaction conditions of substantially greater severity than those maintained in the iirst stage corresponding to an average temperature increase of at least 50 F., and fractionating the desired aromatic compound substantially pure from the mixture thus produced.

6. The process of claim in which the desired aromatic compound is toluene.

7. The process of claim 5 in which the desired aromatic compound is Xylene.

8. The process of claim 5 in which the desired aromatic compound is benzene.

9. A method for producing substantially pure toluene which comprises passing a naphtha including a proportion of non-aromatic compounds containing at least 6 carbon atoms in the presence of added hydrogen in contact at an elevated temperature with an aromatization catalyst to largely convert said non-aromatic compounds to aromatic compounds including a substantial amount of toluene, iractionating the mixture thus produced to separate a toluene-rich fraction including at least 50 per cent toluene together with non-aromatic hydrocarbons containing at least 6 carbon atoms, passing the toluene-rich fraction in contact at an elevated temperature with an aromatization catalyst in the presence of added hydrogen and under reaction conditions of substantially greater severity than those maintained in the nrst stage corresponding to an average temperature increase of at least 50 F., and fractionating substantially uure toluene from the mixture thus produced.

l0. A process for the production of a substantially pure desired aromatic compound which comprises passing a naphtha including a large proportion of non-aromatic compounds containing from 6 to 12 carbon atoms in the presence of added hydrogen in contact at an elevated temperature with a dehydrogenating and cyclicizing catalyst to produce hydrogen and largely convert said non-aromatic compounds to aromatic compounds includinfy a substantial amount of the desired aromatic compound, fractionating the mixture 'thus produced to separate a fraction rich in the desired aromatic compound including at least 50 per cent of the desired aromatic compound together with non-aromatic compounds -rcontaining :6 zorgiimore :carbon atoms, passing v,the thus separated .fraction :rich lthe :desired farozmatic :compound .in contact :at an .average nemperature at least :50 ."liigher than the ancrage temperature maintained in the first stage iwith 4a dehydrogenating and cyclicizing catalystin the Apresence :of `added hydrogen, and Yfractionating the desired aromatic compound substantially pure :from the mixture @thus produced.

11i. n process `ior theiproduction of a vsubsi-,antially pure vdesired aromatic .compound which comprises passing a naphtha including a large proportion .of non-.aromatic compounds containing at least 6 carbon atoms in the presence of added hydrogen inzcoritact at van elevated tem- `.perature with .an .aromatization `catalyst .to .largev'ly convert said non-aromatic-compounds to aromatic compounds including a substantial amount of the desired aromatic compound, fractionating the mixture thus produced to separate a fraction rich in the desired aromatic compound including at least 50 per cent of the desired aromatic compound and including non-aromatic hydrocarbons containing at least 6 carbon atoms, passing the thus separated fraction rich in the desired aromatic compound in contact at an elevated temperature with an aromatization catalyst and under reaction conditions of substantially greater severity than those maintained in the rst stage corresponding to an average temperature increase of at least 50 F., and fractionating the desired aromatic compound substantially pure from the mixture thus produced.

12. In a process for producing substantially pure toluene in which a charging stock consisting essentially of a naphthenic petroleum distillate boiling within the naphtha boiling range is catalytically aromatized by subjection to the action of a, dehydrogenation catalyst comprising molybdena and alumina at a temperature between about 875 F. and about 1075 F. in the presence of a carrier gas containing at least a major proportion by volume of hydrogen, at a total pressure of the order of 50 to 450 pounds per square inch at a mol ratio of hydrogen to naphtha charged between about 0.5 and about 8, and at a space velocity of 0.05 to 5.0 volumes of liquid hydrocarbons charged per volume of catalyst space per hour and thereby a resulting product is produced including toluene and some other constituent undesired in the nnal product and inseparable from said toluene by fractional distillation, the improvement for producing substantially pure toluene which comprisesY fractionally distilling said resulting product and thereby separating therefrom a narrow cut containing substantlally only said toluene in major proportion and constituents inseparable therefrom by fractional distillation and subjecting said narrow cut containing said toluene in the absence of said distillate to the action of a catalyst comprising molybdena and alumina at a temperature between about 900 F. and about 1050 F. in the presence of a carrier gas containing at least a major proportion by volume of hydrogen and a total pressure of the order of from 30 to 450 pounds per square inch and a mol ratio of hydrogen to naphtha charged between about 2 and about 6 at a space velocity of 0.1:1 to 1:1 volume of liquid hydrocarbons charged per volume of catalyst space per hour to transform said cut and render said toluene separable from the transformed product by fractional distillation, the operating conditions in .said second stage being maintained such that about 418 F.

- they correspond to an average temperature increase of at least about 50 F. over those consaid narrow out has a Lboiling range between about 220 F. and about 240 F.

14. The process of .claim 12 in which said naphthenic petroleum distillate has an approximate boiling range between about 240 F. and

' EDWIN T. LAYNG.

REFERENCES CITED Y. The following references are of reeord in the i le of this patent:

12 UNITED 'STATES PATENTS Number Name Date 2,124,567 Grosse July 26, 1938 2,249,337 Visser et ai. July 15, 1941 2,271,751 Visser et a1. Feb. 3, 1942 OTHER REFERENCES Goldwasser et a1., Jour. Am. Chem. Soc., vol. 61, 1766-9 (1939).

Moldavskii et a1., Jour. Gen. Chem. (U. S. S. RJ, vol. VII (LXIX) 169-178 (1937).

Karzhev et al., Khimia Tverdovo Topleva, v01. VII, No. 6, 559-565 (1936) Taylor et al., Trans. of the Faraday Soc., vol. 

1. A METHOD OF PRODUCING SUBSTANTIALLY PURE TOLUENCE WHICH COMPRISES PASSING A NAPHTHA INCLUDING A LARGE PROPORTION OF NON-AROMATIC HYDROCARBONS CONTAINING FROM 6 TO 12 CARBON ATOMS IN THE PRESENCE OF ADDED HYDROGEN IN CONTACT AT AN ELEVATED TEMPERATURE WITH A DEHYDROGENATING AND CYCLICIZING CATALYST TO PRODUCE HYDROGEN AND LARGELY CONVERT SAID NON-AROMATIC COMPOUNDS TO AROMATIC COMPOUNDS INCLUDING A SUBSTANTIAL AMOUNT OF TOLUENE, FRACTIOINATING THE MIXTURE THUS PRODUCED TO SEPARATE A TOLUENE-RICH FRACTION INCLUDING AT LEAST 50% TOLUENE TOGETHER WITH NON-AROMATIC HYDROCARBONS CONTAINING 6 OR MORE CARBON ATOMS, PASSING THE TOLUENE-RICH 